Sound center frequency

During the attenuation measurements. Transducer 1 was excited with a narrowband tone burst with center frequency 18 MHz, see Figure 1 for a schematic setup. The amplitude of the sound pressure was measured at Tranducer 2 by means of an amplitude peak detector. A reference amplitude, Are/, was measured outside the object as shown at the right hand side of Figure 1. The object was scanned in the j y-plane and for every position, (x, y), the attenuation, a x, y), was calculated as the quotient (in db) between the amplitude at Transducer 2, A[x, y), and Are/, i.e., a(x,y) = lOlogm Pulse echo measurements and preprocessing... 

The sound absorption of materials is frequency dependent most materials absorb more or less sound at some frequencies than at others. Sound absorption is usually measured in laboratories in 18 one-third octave frequency bands with center frequencies ranging from 100 to 5000 H2, but it is common practice to pubflsh only the data for the six octave band center frequencies from 125 to 4000 H2. SuppHers of acoustical products frequently report the noise reduction coefficient (NRC) for their materials. The NRC is the arithmetic mean of the absorption coefficients in the 250, 500, 1000, and 2000 H2 bands, rounded to the nearest multiple of 0.05. 

The actual decibel level for the unenclosed condition may be above some desired sound level based on a standard. Call this difference TL. It is common to adjust TL upward by about 5 dB to ensure that the final solution is effective. The total transmission loss TLt the enclosure must achieve is TLg -I- TLg. Then select and analyze enclosure materials and sound-absorbing lining materials to determine the design that is most cost-effective. Repeat this procedure for each octave band center frequency. 

The absorption properties of room finish materials vary with frequency. Manufacturers of sotmd-absorbing materials usually have data on absorption coefficients listed by bandwidth center frequencies. Table 23-4 gives sormd absorption coefficients for selected building materials. The sound absorption for a clothed person in a room varies with frequency and is about 3-5 sabins. 

Octave Band Center Frequency (Hz) Production Area Sound Level (dBA)... 

Fig. 11. Fundamental and harmonic imaging In the fundamental imaging mode (a), a narrow-band pulse of ultrasound (US) centered at a given frequency (e.g., 2.5 MHz) is emitted the sound reflected by the organs is used to create the image, (b) Microbubbles, because they are extremely compressible in comparison to organ tissue, not only reflect sound more efficiently than tissues but also emit harmonics. In the harmonic mode, the signal from the tissues is filtered out, leaving only the harmonics, resulting in specific imaging of the bubbles [37].

Electroacoustics — Ultrasound passing through a colloidal dispersion forces the colloidal particles to move back and forth, which leads to a displacement of the double layer around the particles with respect to their centers, and thus induces small electric dipoles. The sum of these dipoles creates a macroscopic AC voltage with the frequency of the sound waves. The latter is called the Colloid Vibration Potential (CVP) [i]. The reverse effect is called Electrokinetic Sonic Amplitude (ESA) effect [ii]. See also Debye effect. 

Mice were placed into an enclosed chamber with a high-frequency speaker in the center top lid. An audio signal generator was used to produce a continuous sinusoidal tone that was swept linearly in frequency between 8 and 16 kHz once every 10 milliseconds. The average sound pressure level during stimulation was approximately 100 dB at the chamber floor. DBA/2 mice in the vehicle-treated group... 

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